Arsenates and vanadates are poisons which are thought to operate in some instances by mimicing phosphate in biochemical processes. Arsenate has been extensively used to study the sequence of reactions in the process of oxidative phosphorylation, both to gain further insight into the normal mechanisms and to understand the means by which arsenates uncouple the process. Mechanistic models which have been proposed usually involve arsenate esters and arsenatophosphates, but there has been no chemical study of such species under conditions approaching a biological environment. We propose to study the rates of hydrolysis of arsenate and vanadate esters and of condensed arsenates and vanadates and arsenatophosphates as well as the rates of oxygen exchange of arsenate and vanadate with water. We also plan to investigate the nature of phosphate-vanadate solutions to examine the possibility of vanadatophosphates. Because of the possible role of V (IV), we hope to characterize V (IV) species in neutral and basic solutions, and also to study V (IV,V) mixed valence species and V (IV)-phosphate species in solution. The results of these studies should be of fundamental importance to biochemists concerned with poisoning by arsenates and vanadates and with the mechanism of oxidative phosphorylation.